JERUSALEM — Using a lively sense of humor and an unerring feel for the telling anecdote, freed Soviet dissident Anatoly Shcharansky treated 200 journalists and supporters Thursday to a vivid verbal picture of a man locked in a sometimes Kafkaesque nine-year struggle with a system designed to destroy him.

As he described it during a wide-ranging, 90-minute press conference, it is a struggle in which the prisoner tries to put his guards at ease, where the "darkest hour" comes when the promise of freedom for collaboration must be weighed against the threat of execution and where even after the immediate threat of death is past, each man must fashion his own mental defense against physical, moral and psychological breakdown.

The press conference was Shcharansky's first with members of the foreign press since he arrived here Tuesday night, eight hours after walking across the Glienicke Bridge to West Berlin as part of a major East-West prisoner exchange.

The Reagan Administration played the leading role in arranging the swap, and Shcharansky said he plans to express his gratitude with a visit to the United States "as soon as I have enough strength and time."

Shcharansky, who first applied to leave the Soviet Union in 1973 and who became a leading spokesman for both Jewish and human rights activists in Moscow, was arrested in March, 1977, and sentenced in July, 1978, to 13 years in prison and labor camps on charges of being a spy for the United States. He and two American presidents have repeatedly denied those charges.

Earlier Thursday, he underwent three hours of medical tests at Jerusalem's Hadassah Hospital, after which Dr. Marvin Gottesman described him as a man of "extreme psychological and physical power."

Gottesman said that nearly nine years in Soviet prisons and camps have left Shcharansky with a minor heart problem and a tremor in one hand but that all he needs now is rest, dental treatment and exercise.

Speaking mostly in English, Shcharansky told the press conference that the Soviets had begun preparing him for his freedom last Christmas Day, when he was transferred to a prison hospital and put on a regimen of food and vitamin shots that was to add more than 20 pounds to his slight frame in less than seven weeks.

"It's a tradition of the Soviet system that when they produce some goods for export, they put them in much better covering," he quipped.

Asked if he had been tortured during his years in jail, he responded: "If you mean by the word torture beating, physical, no, I wasn't." However, he said, there are other forms of torture--the hunger and cold of a solitary punishment cell or the "moral torture" of absolute isolation.

His most difficult time was in his first months of imprisonment when the Soviets "were trying their best to persuade me that, as they had declared to all the world already, that I am a spy, they had nothing to do but sentence me to death if I wouldn't change my position and wouldn't agree to collaborate."

Idea of Execution

At the same time, he said, the authorities promised "to let me go to Israel if I would cooperate. It was a short period--I think of some months--to get accustomed to this idea that you could be sentenced to death."

Shcharansky, who spent more than 400 days of his nearly nine years' imprisonment in solitary confinement, said that in order to survive such an ordeal "you must have a special kind of psychological exercises."

"It's very individual," he explained. "Everybody must invent it for himself. You must choose the things which are the most important for you and to repeat to yourself these things every day, like a prayer, in order not to forget what is the world like. . . . Because it's just their aim to isolate you so fully, and to create such an image of the outer world that you simply forget--that the system of values, the system of priorities will change."

He said he tried to remember everything he could, including what he knew of Jewish heritage and Jewish songs. "I remember how surprised were those prison guards when the first time they put me in the punishment cell, and almost all the day I was singing."

Shcharansky said he hopes that his 77-year-old mother and older brother, who are still in the Soviet Union, will be able to join him shortly. But he added that he will not remain silent in order to "buy" their freedom.

"I saw many times that when people start negotiating with (the Soviets), they inevitably fail," he explained. "I continued saying whatever I think before the trial, during the trial and in prison, and I'm not going to refuse to do so now.

"I think that as soon as the Soviet authorities will feel that I am more cautious because I don't want to make trouble for my relatives, my relatives will have no chance to leave the country."

Four KGB Guards

Describing the final hours before his release, Shcharansky said that he was flown in a special plane from Moscow to East Berlin last Monday, guarded by four KGB agents.